Lecture 12

Posture and Movement, continued…

 
 

• Caudate Circuit:
  
  • Prefrontal  Premotor  Supplementary motor  Somatosensory  Caudate  Putamen  Globus pallidus
    
    • The Globus Pallidus sends information to the Thalamus.
      
    • The Thalamus will send it back to the Prefrontal and Premotor
      
      • The circuit does not send information to the Primary-Motor cortex because every movement you make has been made before.
        
    • The Caudate Circuit does not plan the movements; you do not have any movements that you have not done before in your life.
      
    • There is a library of movements that are all subconscious.
      
    • This circuit is taking the movements off of the library shelf. You select the patterns of already learned Subconscious motions.
      
    • When you initiate the Subconscious motion – the Caudate Circuit initiates the order in which it should be done.
      
    • Pre-motor also talks to the Neocerebellum (more lateral portion of the cerebellum), which signals back to the Premotor and Supplementary.
      
    • The Neocerebellum is working on the next sequential movement, it is one step ahead.
      

       
       

 

• Movement Execution: performed by the Primary Motor Cortex
  
• The Primary Motor Cortex sends messages from the Upper Motor Neuron to the Lower Motor Neuron, which will go down to the muscle, thus initiating the movement of skeletal muscle
  
  • The Spinocerebellum (in the Basilar Pons) – when the Primary motor cortex sends a message through the Pons to the lower motor neuron it also sends a message to the Spinocerebellum. The Spinocerebellum monitors what information is being sent and it can send corrections back to whatever he thinks might be wrong.
    
    • The Primary Motor Cortex sent a map of what was going on to the Spinocerebellum, which talks back to the Primary Motor Cortex
      
  • The Spinocerebellum sends corrections of its own through the Red Nucleus to the lower motor neuron.
    
    • What the Red Nucleus (in the midbrain) is passing on is monitored by the Spinocerebellum
      
      • A Camel is a horse designed by a committee
        
  • The Neocerebellum is working on the next movement down
    
  • The Floccularnodular Lobe (smallest) – is in contact with Neocerebellum and Spinocerebellum as to equilibrium. They are in connection from the inner ear.
    
    • The Floccularnodular Lobe is working on quicker and more intricate movements that include changes in direction.
      
  • If we make a quick movement that it bypasses the Spinocerebellum (not giving the Spinocerebellum a chance to correct the movement), which is called a Ballistic movement – it will overshoot the target because it does not have a chance to be corrected.
    
    • Ex. Move finger towards the exit fast your arm has a pendulum action (the Spinocerebellum didn't have time to correct it), but if he does it slowly it doesn't waver
      

 
 

Medullary Autonomic Reflex Centers:

• The medulla is the regulator of some fairly complex autonomic nervous system reflexes.
  
• These are also known as Life Centers
  
• 1.) Swallowing:
  
  • Swallowing can be initiated on a Voluntary basis, but it is not always done this way, you are always creating a certain amount of saliva in your mouth and you don't think about it. Once it is started it is finished by an Autonomic reflex.
    
  • The Voluntary stage consists of the tongue pushing upward and backwards.
    
  • Moves the bolus of food into the Oropharynx.
    
  • The uvula pulls the Soft pallet over the nasophayrnx and seals off the nasopharynx so food does not go up your nose.
    
  • Receptors in surrounding epithelium signal the brain and autonomic portion of swallowing starts.
    
  • The vocal cords close and the rise up tightly next to the epiglottis (covering the opening of the larynx) making a tight seal. This shuts off the trachea (which is anterior to the esophagus) so that food doesn't go down this way.
    
  • Respiration is reflexively inhibited.
    
  • The Upper sphincter of the esophagus relaxes.
    
  • The Superior constrictor muscles of the pharynx start a peristaltic contraction.
    
  • This pushes the bolus of food into the esophagus, through the relaxed esophageal sphincter. Peristaltic contractions push the food into the stomach.
    
• 2.) Coughing –
  
  • Coughing is initiated by the irritation of receptors in the pulmonary airways.
    
  • First take a deep breath
    
  • The epiglottis closes and vocal cords push up against the epiglottis and seal off the trachea.
    
  • The Trachialis muscle contracts making the trachea narrower and increases the velocity of the air exiting.
    
  • Intrapulmonary pressure builds, the epiglottis and the vocal cords open quickly and a blast of air comes out through your mouth.
    
• 3.) Sneezing –
  
  • Sneezing is initiated by irritation receptors in the nasal cavity and the nasopharynx
    
  • Similar to cough but the air is directed through your nose.
    
  • The purpose of coughing and sneezing is airway clearance.
    
• 4.) Gagging –
  
  • Gagging is initiated by Oropharyngeal irritation to the point of airway blockage.
    
    • When you stick your finger down your throat to throw up, they will gag, but this is not only due to the irritation receptors but it is always b/c they are blocking their airway when they are doing that
      
• 5.) Vomiting –
  
  • Vomiting is initiated by irritation receptors in the upper GI tract and by chemical receptors (chemoreceptors) in the medulla.
    
  • Reverse peristalsis of the upper GI tract
    
  • Function to empty the stomach.
    

 
 

Homeostasis in the Hypothalamus –

• keeps something normal – maintenance of the body
  
  • ie weight...
    
• http://en.wikipedia.org/wiki/Hypothalmus
  
  
• Hypothalamus plays a role in:
  
  • Sympathetic and Parasympathetic responses.
    
  • It is an integral part of RAS and Limbic system
    
  • It is a part of cyclic behavior.
    
• The Circadian Clock – about a day clock.
  
  • It is located in the Supra-Chiasmatic Nuclei – there are 2 of them
    
    • Each has approximately 10,000 cells and they all function independently of one another.
      
    • Each cell is a clock and it works on the gene level.
      
  • The first gene is called Clock and it makes a protein called Clock.
    

Gene	Protein Produced	Gene Stimulated	Protein Produced
Clock	Clock
BMAL-1	BMAL-1
	Clock + BMAL-1 together	Cryptochrome	CRY
	Clock + BMAL-1 together	Period	PER

• Clock produced all the time (Clock is very easy to find)
  
• BMAL-1 must be stimulated to be produced, so it takes a while to be produced. (It is not made all the time, it must be stimulated)
  
• Clock and BMAL-1 form a heterodimer, and then function as a single protein.
  
  • Together they activate 2 genes – Cryptochrome and Period
    
    • Clock has to get into the nucleus to stimulate these genes.
      
    • As a heterodimer it puts in positive and
      
• CRY and PER bind together to get back into the nucleus, CRY can do it alone, but PER cannot. But once it is in the nucleus, they split apart.
  
  • CRY turns off the heterodimer. This occurs quickly. This is a Negative Feedback System.
    
  • PER helps to slowly stimulate (be positive on) BMAL-1 production.
    
• This on and off cycle will occur in 25 hours, if they are put in a cave where there is nothing (no light whatsoever). They will only be off by one hour each day.
  
• The Circadian clock is corrected to 24 hours by the input of light. This is b/c each of the 10,000 cells (there are 20,000 cells if you count both of the Super-Chiasmatic nuclei) b/c everything is synchronized with the light.
  
• Some of the retinal ganglionic cells go directly to the Supra-Chiasmatic Nuclei
  (SCN) (they don't go to the LGN) – this is referred to as the Retinal-Hypothalamic Tract.
  
  • The ganglion cells of the SCN are releasing Glutamate on the cells, in response to light stimulation (of the rods and cones of the retina)
    
  • The Glutamate can only affect the circadian clock during the phase when the Cryptchrome and the Period are turned off.
    
  • When the Cryptchrome and Period are turned off it is considered to be Circadian Nighttime.
    
  • Light stimulation early in the Circadian Night will move the clock back.
    
  • Light stimulation late in the Circadian Night will move the clock forward.
    
  • Both of these are stimulated by Glutamate but different receptors are involved.
    
  • These corrections resync the clock to 24 hours.
    
  • All 10,000 cells are synchronized because they all received the same light input.
    
  • Both Super-Chaismatic Nuclei are receiving the same light input so they are synchronized together.
    
  • This correction is mainly due to rods and cones, but it can happen in the absence of rods and cones.
    
  • There is a certain ganglion cell (not rods or cones) that has a photopigment called Melonopsin – (this protein can detect a Diffuse light) this is how people do the regulation without rods and cones (blind people). This pigment is in the ganglion cell itself, not in the retina.
    
    • Melanopsin does a very poor job of doing that, and it takes it much longer to reset it with this. It is the light from the rods and cones that is resetting the clock.
      
• The output of the SCN is both electrical and chemical. During Circadian Daytime (heterodimer is active) the SCN will increase its firing rate and is also secreting a signaling protein called Prokineticin 2.
  
  • Increases the amount of Prokineticin 2 it makes during the Circadian Daytime and decreases the amount during the Circadian Nighttime.
    
    • Prokineticin 2 stays within the CNS it only works within the brain.
      
    • The high electrical activity and high production of Prokineticin 2 works the same for Nocturnal (animals that are night active) and Diurnal (animals that sleep at night) animals.
      
      • This is the main clock in our head; it is the one that we worry about resetting. (Jet Lag)
        

• The other body clocks in our body is in our peripheral tissues
  
  
  • These similar clocks are in the
    
    • 1.) Kidney
      
    • 2.) Liver
      
    • 3.) Heart
      
    • 4.) Vasculature
      
  • They are all gene clocks that work in a similar fashion to the SCN circadian clock, but they do not have any direct retina input to reset them; rather they rely on hormone levels to keep them regulated/reset.
    
  • All the peripheral clocks use Clock as a constant level protein of the heterodimer.
    
  • The cyclic protein in all these areas can be BMAL-1 or MOP-4, or some other cyclic protein.
    
  • The variations of the cyclic proteins allow specificity of hormone clock resetting.
    
  • The Peripheral clocks are usually 3 to 9 hours out of sync with the SCN.
    

  Regulation of Meal Intake and Weight Regulation
  

  • Meal Intake – is a short-term homeostatic system; how hungry are you, how much are you going to eat, what makes you start and stop eating (it works on a one meal basis)
    
  • Weight Regulation – is a long-term homeostatic system; how we are going to maintain our stable weight (cycling from the morning to night)
    
    • You weigh the least in the morning and by the time you have gone through the day you will gain 5 pounds, but then you will lose it back again (after a heavy meal you weight more, but when you go to the bathroom you lose weight)
      
    • You will stay within this 5 pound range day after day